The older the Pu'er tea, the greater the risk of carcinogenicity?

The unique selling point of Pu'er tea, the longer it is preserved, the better, while breaking the shelf life constraint, may also open up the risk exposure to food safety.

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Reporter He Tao/Wen Wang Xiao/Editor

An article titled "Can Drinking Tea Prevent Cancer or Cause Cancer?" The popular science article has disturbed a pool of autumn water in the domestic tea industry.

The author of the article is the popular science writer Fang Arkzi. He cites two studies in the article to argue that Pu'er tea on the domestic market generally contains aflatoxin and other mycotoxins, aflatoxin is a carcinogen, therefore, drinking Pu'er tea with aflatoxin has a carcinogenic risk.

Some experts in the tea and food safety community quickly issued a rebuttal, saying that the post-fermentation process of Pu'er tea hardly produces aflatoxin. On September 10, 2017, the Pu'er Tea Association of Yunnan Province held a seminar, and after the meeting, it spoke out through the media, saying that it would formally sue Fangzhouzi, demanding that it make a public apology for its inappropriate remarks and claim 6 million yuan in reputation damages.

This did not shut the mouth of the Ark. He successively refuted the views of the rebuttals one by one, and expanded the scope of the attack on September 11, "All post-fermented teas (black teas) are easily contaminated by aflatoxin, vomatoxin, vomitoxin and other fungal toxins during processing and storage, in addition to Yunnan Pu'er tea, there are also porcelain brick tea, Sichuan border tea, Guangxi Liupao tea, Hubei green brick tea, Hunan Anhua black tea, Anhui Lu'an basket tea... The associations that welcome these teas have come to sue me. ”

In the dust, prosecution is difficult to achieve results in a momentary manner. However, whether the high price of Pu'er tea will bring cancer risks needs to be questioned.

Whether it contains aflatoxin

Back to the origin of the event, the first thing is to clarify whether the Pu'er tea sold on the market contains or does not contain aflatoxin.

In 2010, the Guangzhou Municipal Center for Disease Control and Prevention sampled 70 pu'er tea samples in the local market and found that all of them were detectable for aflatoxin, referring to the 5 μg/kg aflatoxin limit of cereals, and 8 of these samples exceeded the standard.

At the same time, all samples detected vomatoxin and vomitoxin, of which 63 parts exceeded the standard limit of 1 mg/kg.

Vomatoxin mainly pollutes food and its products, and is carcinogenic to humans and animals. Vomitoxin, so named because it can cause vomiting in pigs, poses a threat to the health of humans and animals, especially on immune function. In an evaluation report published by the International Agency for Research on Cancer, vomitoxin is classified as a carcinogen in three categories. The European Union requires vomitoxin to be less than 1.0 mg/kg.

Two years later, Nanchang University also conducted an approximate study. The researchers collected 60 pu-erh teas from the Nanchang market, all of which were able to detect aflatoxin, of which 7 were exceeded; all of them were found to be vomatoxin and vomitoxin, of which 41 were excessive.

Therefore, Fang Arkzi believes that pu-erh tea on the market generally contains aflatoxin and other fungal toxins, and some of them are very high.

Aflatoxin is one of the most carcinogenic substances, and its toxicity of cyanide and arsenic is several streets, which is easy to breed in peanuts, corn and other foods. Once it enters the body through the digestive system, it may cause acute lesions of the liver.

In 2012, the Department of Nephrology of Ma'anshan Central Hospital in Anhui Province reported a case in which a patient brewed 10 grams of Pu'er tea every day to drink, and more than a month later, aflatoxin poisoning led to acute liver damage. It was later found that the aflatoxin content in the Pu'er tea that the patient drank exceeded 30 μg/kg.

However, for the two studies mentioned above that 100% detected aflatoxin, opponents argue that they are not representative.

In 2008, the Food Testing Institute of Shenzhen Institute of Metrology and Quality Inspection undertook the project of "Research on Mycotoxin Detection Methods in Food and Raw Materials" of the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China. According to the article issued by the institute, a thorough investigation was conducted on the mycotoxins in the tea leaves, and no mycotoxin contamination risk was found in the tea leaves. In the subsequent annual national risk monitoring and customer commission inspection, aflatoxin b1 was not found in the tea.

Chen Zongmao, the only academician of the tea industry of the Chinese Academy of Engineering and honorary chairman of the China Tea Society, consulted the papers published in recent years, and statistics showed that scientists from India, Iran, Austria, Germany and other countries analyzed a total of 209 Pu'er tea samples, which were mainly produced in China. ResultsThe aflatoxin was detected in 23 samples with a detection rate of 11%, of which 9 samples had an aflatoxin content of more than 5 μg/kg, accounting for 4.3% of the total sample size.

Research data from China also show that in 2014, the Guangzhou Liwan District CDC randomly purchased 140 Pu'er tea samples from the market, and 8 were detected with aflatoxin, with a detection rate of 5.7%.

Chen Junshi, a researcher at the National Food Safety Risk Assessment Center and an academician of the Chinese Academy of Engineering, said in an interview with the WeChat public account "Public Food Talk" that a comprehensive analysis of these different investigation items should be considered that aflatoxin cannot be said to be detected in Pu'er tea, but at least it will not be a "common phenomenon".

Talking about toxicity out of dose is "hooliganism"?

Different institutions and research teams test different results, why is the gap between the data so large.

The shenzhen institute of metrology and quality inspection officially issued a document on September 6 that the detection of aflatoxin in tea leaves by misinformation on the Internet is likely to be caused by a defect in the standard (detection method). The use of enzyme-linked immunoassay in the old version of the aflatoxin b1 test standard is easy to judge samples that do not originally contain aflatoxin as containing aflatoxin, resulting in errors in the results.

These detection vulnerabilities have been revised in the latest version of the standard, which came into effect on June 23, 2017.

However, this statement also needs to be more rigorous, that is, the error of the enzyme-linked immunoassay has both positive and negative sides, that is, it may judge the sample that does not contain aflatoxin as containing aflatoxin, and the higher content of aflatoxin may be measured low or even undetected.

At this moment, Fang Arkzi successively revealed "two new evidences". First, a team led by Xu Kunlong, vice president of Yunnan Agricultural University, published in international journals in 2015, took 15 raw teas and 15 cooked teas from 15 tea factories in 5 regions of Yunnan, all of which were found to be aflatoxin, with content higher than the allowable values in the European Union, the United States and Japan. As of press time, caijing reporters have not received a reply from Xu Kunlong.

The second evidence is a paper published in an international journal by the Institute of Oilseeds of the Chinese Academy of Agricultural Sciences in 2011, in order to study the detection technology of aflatoxin, they sampled peanuts, Pu'er tea, vegetable oil, feed and other samples from the market, of which a total of 5 Pu'er tea samples were found, all of which found aflatoxin, up to 59 ng/g (equivalent to 59 micrograms/kg), higher than all peanut samples.

Both studies used a detection method called high performance liquid chromatography (hplc), which first isolated the aflatoxin contained in the sample, purified it, and then quantitatively determined it, eliminating error problems and greatly improving the measurement accuracy.

There is also a strange difference, Fang Arkzi said, "The export of tea countries require the check of aflatoxin, the country itself drinks but does not check, listening to it is not right." ”

According to the requirements of the General Administration of Quality Supervision, Inspection and Quarantine, when tea, including Pu'er tea, is sold abroad, aflatoxin testing should be done, in accordance with the industry standard of "Determination of Aflatoxin Residue in ExportEd Food", and it is almost unnecessary to do it when selling in China.

Oncology expert Wang Chenguang told Caijing that the current questioning of Fangzhouzi is based on officially published data, rather than fabricated data. As long as the research methods are reliable, the sampling is representative (regional representation is ok), and the data are authentic, "even if there is only one study, it can be questioned."

This shows that for the huge lineup of Pu'er factions now, if you want to truly prove that Pu'er tea is not worried about food safety, you must first overturn the data of these research papers.

Almost unanimously, many experts in Pu'er have focused on the dosage of aflatoxin, that is, although some Pu'er tea on the market may be contaminated with aflatoxin, Pu'er tea can still be drunk with confidence.

Yun Wuxin, a doctor of food engineering at Purdue University in the United States, believes that from "detecting aflatoxin" to deduce "drinking Pu'er tea to cause cancer", it is a typical "rogue behavior of talking about toxicity without dose". The concentration of aflatoxin in Pu'er tea is very low and it is unlikely to cause acute poisoning. Its main harm is that long-term intake will increase the risk of liver cancer. But this increased risk may be equivalent to only one percent of the carcinogenic risk of a person consuming aflatoxin from food.

After the Guangzhou CDC's paper on the detection of aflatoxin in Pu'er tea was reported by the media in 2010, experts from domestic authoritative institutions carried out targeted scientific evaluations. Chen Junshi revealed that the results show that even if consumers drink Pu'er tea that is within the limits of aflatoxin contamination every day, it will not cause liver cancer.

However, the World Health Organization states that aflatoxin, as a carcinogen, should be ingested as much as possible, and that the aflatoxin limit in food testing standards is only for management and cannot be considered a safe value. In fact, many times humans do not study the toxicity of many substances clearly enough, and the dose relationship between it can cause harm to people is not known.

According to this, Fang Arkzi believes that unlike staple foods, Pu'er tea is non-essential for humans, and other tea varieties can be completely replaced, so why risk ingesting carcinogens for no reason? He also said that foods containing carcinogens are not necessarily untouchable at all, but they need to understand their risks and make a trade-off between delicious and healthy.

Pu'er tea should also have a shelf life?

There is a huge "black hole" in the process of Pu'er tea - there is no concept of shelf life.

The vast majority of food will be clear "ready to eat", consumers also have this common sense, once the food packaging is opened, it should be eaten as soon as possible, otherwise the quality will become worse, or even deteriorate. Pu'er tea is just the opposite, and the old Pu'er tea will be considered to be of excellent quality and mellow taste.

From the production process, Pu'er tea needs to go through the open post-fermentation stage, and it must be fermented non-stop in preservation, can not be baked and sterilized, nor can it be vacuum sealed, and is generally packaged in paper.

In fact, many foods are produced through fermentation, such as wine, yogurt, cheese. However, in order to avoid harmful fungal contamination, these foods should strictly control fermentation conditions, often inoculate beneficial fungi, and inhibit harmful fungi through the proliferation of beneficial fungi.

Fang Ark zi questioned that Pu'er tea is "natural fermentation", neither controlling the conditions nor inoculating beneficial bacteria, how can it be guaranteed to be free of mycotoxins?

Fermentation is also affected by geographical, climatic and other conditions. For example, in a very narrow east-west region of China, bacon and ham can be concocted, but if it is dried in other regions, it can easily become stinky meat. The aged Pu'er tea can be applied in a wide range of parts of the country and deserves further study.

Some netizens argue that this is like some high-end wines also have the concept of cellaring, the longer the more fragrant. But there is an important condition here, the mouth of the bottle must be sealed to isolate the air and avoid the oxidation of the wine. Pu'er tea, on the other hand, is mostly packaged in simple paper, and tea cakes can be freely in contact with the outside air.

Under the concept of the older the better, people who drink Pu'er tea will usually buy Pu'er tea and store it for a long time. The average person does not have a particularly good storage environment, which also causes the longer the storage time, the higher the probability of problems.

If there is a trace of Aspergillus aflex on the tea cake, over time, aspergillus aflex will continue to grow; even if the tea cake is not contaminated with Aspergillus aflatoma, but the longer it is stored, the greater the possibility of encountering accidents in the process, such as experiencing a longer period of wet weather, the higher the probability of pollution of Aspergillus aflatoma.

A researcher engaged in biological research at the Chinese Academy of Sciences told Caijing that pu'er tea is more expensive and more expensive, which violates science and increases risk factors. In his view, in order to study the problem of aflatoxin in the aging Pu'er, it is necessary to pay attention to the situation of Pu'er tea when consumers drink.

Fang Ark Zi did not beat Pu'er tea to death, "Drink fresh Pu'er tea, there is no problem." ”

This storm is still stirring up by all parties, but if it can be used to promote the standardized management of China's tea industry, such as the promotion of aflatoxin testing in tea in China, it is a good thing for public health.